1. Technical Field
The invention generally pertains to ink jet printers, and particularly, to such printers using a binary imaging solution and multiple drop size ink jet print head technology.
2. Description of the Prior Art
A binary imaging solution uses colorants that each comprise a mixture of two ink components, where the two components are combined at the time the colorant is applied to a recording surface. Traditionally, to use a binary imaging solution in an ink jet printer, one channel of colorant per channel of reactant is used to ensure proper mixture of the two-part solution. This implementation, although feasible, has never really seen wide range adoption due to the cost associated with ink jet print head assemblies. In effect, this implementation would require double the number of print heads as compared to a uniary imaging solution.
As the demand for higher print quality and speeds has progressed in digital ink jet printing, print head technology has progressed in kind, starting from airbrush technology, having print resolutions of 4-9 dpi, to the newer drop-on-demand ink jets, having print resolutions up to 2400 dpi. At the older resolutions of sub-10 dpi it did not take many print heads to deliver acceptable printing speed considering that the size of the printed dot was 1/10 of an inch. Now consider that to generate images in the range of 1200 dpi the drop size would need to be 1/1200 of an inch. When working with drop sizes so small it takes many more drops to get an acceptable fill pattern when working with solid colors. This can only be accomplished in one of two ways: populate more ink jets into the product to increase coverage per pass of the print head array; or interlace many more print head passes of the print head array with the same number of print heads.
The first option would drive up printer cost to an unacceptable level, while the second option would drop productivity to unacceptable levels.
With the advancement in print head technology into grey scale functionality, the print head technology for grey scale functionality has provided an answer to this issue. These print heads generate multiple drop sizes from the same nozzle assembly. Therefore, one can generate a larger drop size when a good solid fill pattern is needed and a smaller drop size when higher detail is needed.
Prior to the introduction of grey scale print head technology the application of a binary imaging fluid was somewhat hampered also. For example, a traditional ink jet printer may have four color channels, including Cyan, Magenta, Yellow and blacK (CMYK). Other color channels employing colors such as White, Blue, Red, Orange and Green may also be used to increase functionality and color gamut. For these examples it is assumed that a printer uses seven color channels, one each for Cyan, Magenta, Yellow, blacK White, Blue, and Red, (CMYKWBR).
In traditional methods, for the application of binary solutions one of two options is selected. The first option is to use only one channel of reactant (CMYKWBRr), whereby one drop of reactant is applied to a location in an ‘OR’ methodology, where it would be applied to any drop location that is slated to receive, or already has received, a colorant drop. This method, although acceptable for a surface preparation type of implementation or an over coating application, is not effective for accurate metering of the binary mixture ratio. This is because each printed location could have anywhere from one to seven colorant drops placed in that location and only one drop of reactant. The ratio of reactant to colorant drops, assuming similar drop sizes, could be anywhere from 1:7 to 1:1. This is the method taught by Allen (U.S. Pat. No. 5,635,969), whereby the reactant channel is used as a pre coat for the colorant to control dot gain and other print artifacts.
A second option would be to have one channel of reactant per channel of colorant to provide for accurate mixing of the solution (CrMrYrKrWrBrRr). To provide the same speed and functionality as the previous example it would require 14 separate channels to provide accurate ratio metering at speed. This method is taught by Vollert (U.S. Pat. No. 4,599,627), whereby every drop of colorant is matched to a single drop of reactant to ensure a consistent ratio.
Although this solution is functional in providing an accurate mixture of the binary solutions in a controlled ratio, it is largely cost prohibitive due to the volume of additional print heads needed and ancillary equipment needed to support them as compared to uniary print systems.
Thus, a heretofore unaddressed need exists in the industry to address the aforementioned deficiencies and inadequacies in connection with binary imaging.
Traditionally, in the wide format ink jet market, in order for printers to utilize a wide variety of print medias desired by the customer base, it is necessary to print with a UV curable ink. However, there are often health and safety issues related to the use of the UV curable ink products.
It would therefore be advantageous to provide more environmentally friendly inks, with ultra-low VOCs and no HAPs. The development of such inks would be constitute a significant improvement over prior ink technologies.
Some conventional systems for media transport comprise two coaxial rollers, with a belt stretched between them. If and when such a system is perfectly square, this configuration may be adequate. However, belts are often not square, such as due to manufacturing processes involved with making them.
In such as design, a consistent tension is needed across the width of the belt, for the belt to track properly, and not try to run off the end of the assembly. To provide tension in a dual roller system with a belt that is not perfectly square, one of the rollers, referred to as a tension roller, is required to be skewed in relation to the second, stationary roller, to provide consistent tension across the belt.
While such a structure may prevent the belt from working its way off the end of the assembly, this approach inherently introduces another, more difficult problem. While the tension applied across the belt may be consistent, the stationary roller and the tension roller are longer parallel to either each other and to the media that is being transported, wherein such a system tends to skew and wrinkle the media, making it very difficult to print, and increases the danger of head strikes, i.e. direct contact between one or more print heads and the media.
It would therefore be advantageous to provide a media transport system that can compensate for less than perfect drive belts, while retaining a belt path that is parallel to a printing media. Such a system would constitute a significant technological advance.
To provide sufficient belt tension across a span of greater then 1.5 meters, conventional rollers have previously been large in diameter, with heavy walls and internal support structures. Such rollers are often prohibitively expensive and complex, to avoid deflection in the middle of the roller.
Alternate systems have been used to avoid such deflection, wherein a backer roller contacts the main roller, and supports the main roller from the rear, in a location that supports the main force of deflection. Such approaches often require a non-coated metal section of the roller where the backer rollers support the system. This adds to the cost of the roller, and often has wear issues that require frequent service and replacement.
It would therefore be advantageous to provide a more cost effective and robust roller system, which adequately minimizes deflection. Such a system would constitute an additional technological advance.
In prior media transport systems for inkjet printers, a vacuum table is typically placed under a transport belt, to hold the print media flat and true while the print heads traverse over the media. However, the amount of vacuum needed to hold media flat can sometimes provide so much drag on the system that the media transport motor can no longer accurately step the belt, due to limits in its ability to overcome the torque and force required. The media can also become warped, such as due to a number of reasons, including storage issues and heat applied during the print process.
It would therefore be advantageous to provide an enhanced structure and associated process that provides accurate retention of media without undue stress, as well as accurate movement of the media. Such an improvement would constitute a significant technological advance.
In typical grand format printing systems, the carriage is mounted to a rail system on a series of slide rails and bearings, in a cantilevered fashion. Because of this, the length of the inkjet array is typically limited by the manufacturing tolerances involved with the straightness and parallelism of the rails. For printing systems that comprise two independent rails, the associated support structures can cause a number of challenges, particularly in regard to the straightness and parallelism of the two rails.
It would therefore be advantageous to provide a rail system for a printer, e.g. a grand format printer, which reduces telebanking and manufacturing issues associated with straightness and parallelism of the rails. Such a system would constitute a major technological advance.